docs: fix link to rustdocs
docs: fix link to rustdocs

Now that we are generating docs for changes coming into
master, it is probably best to have docs that are up-to-date.

Signed-off-by: Paul Osborne <b6afffd6c1a00645fdd04b09edf63d034a949a39@gmail.com>

nastevens/rust-sysfs-gpio,marjakm/rust-sysfs-gpio,rust-embedded/rust-sysfs-gpio